The present invention relates generally to imagers having a focal plane array of infrared detectors and charge coupled device signal processing circuitry associated with the detectors to transfer the signals produced by the detectors into data processing apparatus. Here the image may be reconstructed from the signals in a manner determined by the particular mode of scanning employed. Imagers of this general type are disclosed, for example, in the following U.S. Pat. Nos.:
B. K. Weimer--3,683,193 PA1 Y. Takamura--3,777,061 PA1 D. R. Collins--3,771,149 PA1 K. Nummedal--3,883,437.
In the prior art, of which the foregoing patents are typical, efforts to integrate the photodetectors of such an array with charge coupled circuitry have in the past led either to hybrid devices wherein the detectors were mounted on top of a separate semiconductor substrate in which the charge coupled circuitry was contained or to an arrangement wherein the photodetectors were formed as portions of the same semiconductor substrate containing the charge coupled circuitry.
The device disclosed and claimed in our copending application Ser. No. 614,277 represents a successful monolithic integration of the detector and its associated CCD circuitry into one efficient and low-cost device. In the fabrication of our earlier structure disclosed in Ser. No. 614,277, an epitaxial layer is formed on an IR detector substrate and then a portion of that epitaxial layer is etched away as to permit infrared radiation to impinge on the individual detectors of the substrate. This construction produces charges which are then read out by direct injection into the charge coupled device which is built on the epitaxial layer and functions to transfer charges through the epitaxial layer and into the output of the device.
The device disclosed and claimed in our copending application Ser. No. 702,548 eliminates the need for having a portion of the epitaxial layer etched away. It instead uses different means for collecting charges generated in the detector elements and injecting them into the CCD circuitry. Among the charge collection structures disclosed was the use of a conducting buried layer and conducting surface layer combination for the collection and transfer of charges from the detector elements to the CCD circuitry.
We believe that our inventions disclosed and claimed in the aforementioned patent applications represents truly significant advances in this art as explained in detail in said applications. Our present invention extends the developments in this area of technology and has the further advantages of improving the fill factor with either frontside or backside imaging, maintaining a uniform electric field distribution in the detector region and improving the isolation of the CCD operation from the extrinsically doped substrate.